So what stops you from pressing that send button for an e-mail that tells off your boss? Three distant brain regions connected by “hyperdirect cables,” believe scientists at the University of California, San Diego. They asked participants to plan an action, listen for a stop signal and decide whether to obey or continue as planned. Brain scans revealed that a neural braking network kicks in for a few milliseconds—just long enough for participants to make a decision. The inferior frontal cortex sends the braking signal to the midbrain's subthalamic nucleus, which stops motor movement; a third region, the presupplementary motor area, initiates the plan to halt or continue the action. No synapses lie between the areas, enabling direct and fast communication. Understanding this network could explain neurological disorders such as stuttering, which may arise from the brain's inability to coordinate stop signals. The work appears in the April 4 Journal of Neuroscience.
This article was originally published with the title "Brain Brakes" in Scientific American 296, 6, 38 (June 2007)